Year	Percent
1960	6.47853
1961	6.51935
1962	6.57457
1963	6.64665
1964	6.74467
1965	12.34668
1966	12.60342
1967	12.29673
1968	11.96958
1969	11.58679
1970	11.2113
1971	10.81131
1972	10.40324
1973	9.93057
1974	7.10408
1975	6.67504
1976	6.45821
1977	6.24184
1978	6.08183
1979	5.97784
1980	5.90151
1981	5.82572
1982	5.71982
1983	5.53061
1984	5.25455
1985	3.53418
1986	3.14388
1987	2.91378
1988	2.72977
1989	2.61096
1990	2.52988
1991	2.46829
1992	2.39364
1993	2.28864
1994	2.14634
1995	1.9846
1996	1.81546
1997	1.68993
1998	1.62098
1999	1.62204
2000	1.67002
2001	1.72165
2002	1.75138
2003	1.76852
2004	1.76548
2005	1.73865
2006	1.74462
2007	1.73857
2008	1.62745
2009	1.38043
2010	1.05837
2011	0.68197
2012	0.37653
2013	0.27338
2014	0.452
2015	0.82577
2016	1.27069
2017	1.63223